Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. To be more specific, the present invention relates to a technique of reducing noise in image data.
Description of the Related Art
The sensitivity of a camera is desired to be increased from those of conventional ones to capture darker scenes and subjects moving at a higher speed than before. However, since increasing the sensitivity of a camera increases noise, a noise reduction process for attenuating noise at a greater degree is required. In a case where the noise reduction process is performed by simple averaging or the like, the resolution of an image deteriorates. In view of this, techniques for reducing noise while preserving edges and textures are laid open (for example, Japanese Patent Laid-Open No. 2010-245977 and Japanese Patent Laid-Open No. 2007-536662). In these noise reduction techniques, a weighted mean value is calculated by calculating similarity between a target pixel for which noise is to be reduced and each of reference pixels around the target pixel, and then determining a weight according to the similarity. Then, the value of the target pixel is determined by using the weighted mean value.
However, in a case where the weighted mean value is calculated by calculating the weight according to the similarity based on the target pixel as described above, the mean value is affected by the noise included in the pixel value of the target pixel itself. Hence, such a technique has a problem that the weighted mean value converges not at a true pixel value of the target pixel but at a value different from the true pixel value without noise, even if the number of reference pixels is increased, and this appears as remaining noise.